首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   134篇
  免费   6篇
  国内免费   23篇
安全科学   1篇
环保管理   28篇
综合类   57篇
基础理论   37篇
环境理论   1篇
污染及防治   16篇
评价与监测   7篇
社会与环境   6篇
灾害及防治   10篇
  2022年   5篇
  2021年   10篇
  2020年   8篇
  2019年   6篇
  2018年   6篇
  2017年   4篇
  2016年   4篇
  2015年   5篇
  2014年   5篇
  2013年   13篇
  2012年   5篇
  2011年   10篇
  2010年   5篇
  2009年   6篇
  2008年   5篇
  2007年   9篇
  2006年   10篇
  2005年   6篇
  2004年   3篇
  2003年   2篇
  2002年   3篇
  2001年   7篇
  2000年   3篇
  1999年   4篇
  1996年   1篇
  1995年   1篇
  1993年   3篇
  1992年   2篇
  1990年   1篇
  1988年   1篇
  1986年   2篇
  1985年   2篇
  1984年   4篇
  1983年   1篇
  1979年   1篇
排序方式: 共有163条查询结果,搜索用时 125 毫秒
131.
132.
Changes in a range of interlinked factors, in social, economic, environmental and climatic conditions, require adaptation in many communities. This paper explores how place attachment affects adaptive responses to a changing social context through analysing adaptation in two coastal municipalities in Northern Norway. The main challenge in these municipalities is declining populations and the consequences accompanying this trend, including livelihood uncertainties and decreased provision of public services. This paper discusses the role of place attachment in motivating adaptation to these changes to contribute to a growing body of literature within climate change adaptation on “subjective” (values, culture and place) dimensions. The findings suggest that people are motivated to act based on their emotional connection with place, and the paper argues that place attachment may offer a better starting point for climate change adaptation than an emphasis on climate change impacts.  相似文献   
133.
近20 a陕北地区耕地变化及其对农田生产力的影响   总被引:1,自引:0,他引:1  
陕北地区耕地开垦和生态保护与建设工程等对耕地资源的空间分布格局产生了重要影响,并进一步影响农田生产力。论文基于中高分辨率卫星遥感数据,经人机交互目视解译和实地验证,生成陕北地区1990、2000和2010年耕地现状以及前后两个10 a耕地动态数据集。利用光能利用率遥感模型,结合中分辨率、长时间序列卫星遥感数据估算陕北地区农田净初级生产力,分析耕地变化对农田生产力的影响。结果表明,陕北地区耕地面积及其生产力在研究期前10 a小幅增长,后10 a明显减少。耕地减少的最主要原因是生态退耕,城市化也是耕地减少的原因之一。总体而言,20 a来,陕北地区耕地资源总面积净减少42.56%;受耕地面积变化的影响,同期农田净初级生产力下降了41.90%。研究对于评估陕北地区耕地安全和粮食安全,指导区域土地利用科学规划,具有重要意义。  相似文献   
134.
黄河变迁史上的第三次大改道导致黄河突发北徙,彻底改变了泛滥区城市的自然和人文环境,是开展复杂人地耦合系统研究的理想区域。利用水平横剖面法、数理统计与GIS手段相结合的方法,探索黄泛城市的数目、时空变化特征和适应性类型。结果表明:(1)黄河7个行河期的决溢泛滥,产生29座受灾城市;(2)受灾城市总体分布广泛,但又相对集中分布在黄河决口所形成的洪积扇顶部附近,地势低洼的冀中平原以及黄、御等河流交汇处;(3)黄泛城市主要呈现出避河患迁城、因河患省并、原址加固防御、直接湮废四种适应性类型,以避河患迁城型居多,占45%;(4)朝廷政策和城市规模是影响城市在黄河突发灾害下的空间分异和适应性举措的重要人文因素。黄泛区受灾城市具有重要的地方性保存和可持续发展演进模式。建议将其纳入“黄河流域生态保护和高质量发展”国家战略,作为讲好黄河故事的重要区域。  相似文献   
135.
The present study objective was to investigate ratios and correlation coefficients between dichlorodiphenyltrichloroethane (DDT) compounds in cord and maternal sera of mother-infant pairs from northern Thailand. The study site was located in Chiang Dao District of Chiang Mai Province which was an agricultural and former malaria endemic area. DDT compounds were analyzed in 88 cord and maternal serum samples using gas chromatography-electron capture detection (GC-ECD). p,p′-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) was the major component and detected in every cord and maternal serum samples with geometric means of 1,255 and 1,793 n g?1 lipids, respectively. p,p′-DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) was detected at 89.8 and 100% of cord and maternal serum samples, respectively. The second and third highest levels detected were p,p′-DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) and p,p′-DDT, respectively. The ratios between cord and maternal sera for p,p′-DDE, p,p′-DDT, and p,p′-DDD that were less than 1 had high correlation coefficients (ratio = 0.70, r = 0.82 for p,p′-DDE, ratio = 0.62, r = 0.66 for p,p′-DDT, and ratio = 0.79, r = 0.78 for p,p′-DDD). The high correlation coefficients indicate that cord serum levels of DDT compounds could be accurately estimated from maternal serum levels. It can be concluded that cord serum levels of p,p′-DDE, p,p′-DDT, and p,p′-DDD were approximately 70%, 62%, and 79% of maternal serum levels, respectively. Furthermore, our findings can be applied in public health to monitor and evaluate risk among infants from high DDT exposure area.  相似文献   
136.
ABSTRACT

Water shortages may present different and diverse implications for gender subgroups particularly in low-income settings. Yet, little research has documented the gendered livelihood implications of water shortages in Ghana. Based on a cross-sectional mixed method research involving a survey of 250 household heads and complemented with a qualitative study of 86 participants, the paper examines the differential effects of sporadic water supply in Tatale-Sanguli District of Northern Ghana. Our findings suggest that the livelihood effects of sporadic water supply in Tatale-Sanguli area are gendered, with females being disproportionately affected as compared to males. These differential effects are often framed by both gender role differentiation and inequities in access to vital productive resources and critical assets such as bicycles, tricycles and motor bikes. These findings highlight not only the need for local government and non-governmental organisations to step up efforts in water provision, but also to recognise the gendered effects of water shortages in Tatale-Sanguli District. Key to policy is also to ensure that programmatic interventions during water shortages take account of the likely gendered effects and differentiated burdens.  相似文献   
137.
Abstract:  Although species with large area requirements are sometimes used as umbrella species, their general utility as conservation tools is uncertain. We surveyed the species diversity of birds, butterflies, carabids, and forest-floor plants in forest sites across an area (1600 km2) in which we delineated large breeding home ranges of Northern Goshawk ( Accipiter gentilis ). We tested whether protection of the home ranges could serve as an effective umbrella to protect sympatric species of the four taxa. We also used an empirical habitat model of occupancy of home range to examine mechanisms by which the Northern Goshawk acts as an umbrella species. Among species richness, abundance, and species composition of the four taxa, only abundance and species composition of birds differed between sites located inside and outside home ranges, which was due to greater abundance of bird species that were prey of Northern Goshawks inside the home ranges. Thus, although home range indicated areas with high abundance of certain bird prey species, it was not effective as an indicator of the species diversity of all four taxa. We also did not find any difference in species richness, abundance, and species composition between sites predicted as occupied and unoccupied using the habitat model. In contrast, when we selected sites on the basis of each habitat variable in the model, habitat variables that selected sites either in agricultural or forested landscapes encompassed sites with high species richness or particular species composition. This result suggests that the low performance of the Northern Goshawk as an umbrella species is due to this species' preference for habitat in both agricultural and forested landscapes. Species that can adjust to changes in habitat conditions may not act as effective umbrella species despite having large home ranges.  相似文献   
138.
In much of sub-Saharan Africa (SSA), the lack of organic soil amendments constitutes one of the principal causes for declining soil fertility in intensifying farming systems. The challenge, therefore, remains to increase the availability of organic inputs and to develop recommendations for their combination with inorganic fertilizers. An on-farm experiment was conducted in the northern Guinea savanna of Nigeria to evaluate the fertilizer effect of rice (Oryza sativa L.) mill waste (RMW) on a degraded Alfisol. The decomposition and nutrient (N and P) release patterns of RMW were studied using the litterbag technique, and the effect on maize yield and soil properties was determined. The RMW was applied at rates of 0, 5, 10, and 15 Mg DM ha−1 and was applied either unburnt or burnt (farmers’ practice). In both years, compound fertilizer was broadcast during land preparation on all plots at rates of 40 kg N ha−1, 17 kg P ha−1, and 33 kg K ha−1.Results obtained in the litterbag study showed that, at maize harvest, more than 90% of the P had been released from the decomposing RMW. However, around 60% of the organic C and 45% of the N still remained. Compared to the control treatment (0 Mg ha−1 RMW), which yielded 0.55 Mg ha−1, maize (Zea mays L.) grain yields were increased by 95% when 10 Mg ha−1 of unburnt RMW was applied, and by 147% with 15 Mg ha−1 (mean of 2 years). In contrast, burnt RMW did not result in significant yield increases. The cumulative application of 30 Mg ha−1 of unburnt RMW significantly increased the soil organic carbon in the surface soil from 0.7% (0 Mg ha−1 RMW) to 1.3%.The results of this investigation indicate that RMW constitutes a valuable organic input in the Guinea savanna if applied unburnt at rates of 10–15 Mg ha−1 in combination with inorganic fertilizer. The repeated application of unburnt RMW may contribute to the rehabilitation of degraded soils through the buildup of soil organic matter.  相似文献   
139.
Abstract:  Ecologists often discount presence-absence surveys as a poor way to gain insight into population dynamics, in part because these surveys are not amenable to many standard statistical tests. Still, presence-absence surveys are sometimes the only feasible alternative for monitoring large areas when funds are limited, especially for sparse or difficult-to-detect species. I undertook a detailed simulation study to compare the power of presence-absence, count, and time-to-encounter surveys to detect regional declines in a population. I used a modeling approach that simulates both population numbers and the monitoring process, accounting for observation and other measurement errors. In gauging the efficacy of presence-absence surveys versus other approaches, I varied the number of survey sites, the spatial variation in encounter rate, the mean encounter rate, and the type of population loss. My results showed that presence-absence data can be as or more powerful than count data in many cases. Quantitative guidelines for choosing between presence-absence surveys and count surveys depend on the biological and logistical constraints governing a conservation monitoring situation. Generally, presence-absence surveys work best when there is little variability in abundance among the survey sites, the organism is rare, and the species is difficult to detect so that the time spent getting to each survey site is less than or equal to the time spent surveying each site. Count surveys work best otherwise. I present a case study with count data on the Northern Flicker ( Colaptes auratus ) from the North American Breeding Bird Survey to illustrate how the method might be used with field-survey data. The case study demonstrates that a count survey would be the most cost-effective design but would entail reduction in the number of sites. If this site reduction is not desirable, a presence-absence survey would be the most cost-effective survey.  相似文献   
140.
In a field experiment on the island of Helgoland (southeast North Sea), we investigated whether migration strategy or competition between the sexes cause the differential timing of spring migration of male and female northern wheatears (Oenanthe oenanthe) (males migrating earlier). The study included two subspecies, heading towards Greenland/Iceland and Scandinavia, respectively, and is based on colour-ringing and remote weighing of individuals. Despite food offered ad libitum, most Scandinavian birds left the island on the day of arrival or stayed only 1–3 days, whereas more than half of Greenlandic/Icelandic birds stayed for up to 12 days and refuelled rapidly. In the latter subspecies, males showed a positive correlation of departure fuel load and fuel deposition rate, resembling time-minimizers in optimal migration theory. In contrast, females departed irrespective of fuel deposition rate, with an approximately constant level of fuel stores. This level was lower than in males, but sufficient to enable by-passing of stopover sites en route, allowing us to regard females as time-minimizers also. Since females are not able to reach Greenland without additional refuelling elsewhere and males appeared to have a larger potential for by-passing stopover sites, time-selection seems to be more pronounced in males and may be the reason for earlier migration of males. Intraspecific aggressive interactions between colour-ringed birds were predominantly won by the initiator, by males and by larger birds, whereas fuel load and subspecies did not affect the outcome. Although compared to females, males were more often dominant at the feeding stations or held territories, refuelling patterns could not be explained by dominance. Subordinate or non-territorial birds did not refuel at a lower rate or depart with lower fuel loads than dominant or territorial birds. In non-territorial birds, the restricted access to feeding stations was made up with larger doses of food taken per visit, leading to the same energy intake as that of dominant and territorial birds. Therefore, competition during stopover could be eliminated as the reason for differential timing of migration of male and female wheatears, but this result may be species-specific.Communicated by W. Wiltschko  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号